This invention relates to ink jets, and more particularly, ink jets of the demand type or impulse type.
Ink jets of the demand type include a transducer in one form or another which is coupled to a chamber adapted to be supplied with ink. The chamber includes an orifice for ejecting droplets of ink when the transducer has been driven or pulsed by an appropriate drive voltage. The pulsing of the ink jet abruptly reduces the volume of the jet so as to advance the meniscus away from the chamber and form a droplet of ink from that meniscus which is ejected away from the ink jet.
In order to achieve the formation of the droplet by the sudden reduction in volume of the ink jet chamber, the pulse which is applied to the transducer has an extremely steep fall time (or rise time). U.S. Pat. No. 4,104,646--Fischbeck discloses the typical pulse shape utilized in driving a demand ink jet.
The achievement of high speeds in ink jet printing has been somewhat of a problem. High speeds in ink jet printing require that demand ink jets operate on an extremely high droplet projection rate. This in turn requires some control of the meniscus between droplet projections so that each droplet will be projected from the ink jet at the exact moment the droplet is called for. In order to achieve some control of the meniscus, it has been proposed in the above-mentioned Fischbeck patent, as well as U.S. Pat. No. 4,112,433--Vernon, that the transducer be driven with a secondary pulse immediately after projection of the droplet so as to damp the meniscus. However, filling of the chamber after the meniscus has been damped can still result in uncertainty and mislocation of the meniscus at the time of firing or droplet projection which occurs sometime later.
Other problems associated with demand ink jets include low droplet velocities, incorrect drop size and production of undesirable satellite droplets. Problems are only compounded when an array of ink jets are utilized where it is desirable to achieve the same droplet projection characteristics from jet to jet.